All,

I have been using similar combinations with the f/3.3 reducer on a
LX200 and a ST7. In one case I used a 15mm spacer and the effective f
ratio was 4.2 with some slight distortion towards the side and
vignetting.

Presently I have added a filterwheel (directly mounted on a ST7 XME)
and used the minimum adapter size possible. It gives an effective f/3.7
but the distortion to the 'long' sides is considerably worse with
elongated (comatose) star images. This effect is not symmetrical wrt the
image centre.

It is a nuisance but the larger field makes up for it re my
applications.

By slightly cutting the water cooling connectors and removing the fan
grid I am even able to move the CCD system with filter wheel through the
fork...

Berto Monard
Bronberg Observatory

Lawrence,

You really don't want to reduce more than f/5, or you will get a lot
of
distortion. For me, that meant using no spacers, as the distance
supplied
by the filter wheel and the camera was just right. About half of the
pictures on my website were taken with an ST-7E using the .33 reducer,
spaced for f/4.6, and very little distortion shows.

Mark de Regt
Redmond, Washington, USA
47.7 N. Latitude; 122 West Longitude
Astro Images: http://home.earthlink.net/~akilla/MAD


> -----Original Message-----
Of
> Lawrence
> Sent: Wednesday, March 31, 2004 10:21 AM
> Subject: RE: [M]: using the f3.3 reducer
>
>
> >Subject: RE: [M]: using the f3.3 reducer
> >
> >What size chip are you using?
> >Even with a relatively small chip, uneven illumination is
> obvious when using
> >a 3.3 reducer. Correcting with a flat field image is basically
> a necessity.
> >- -John
>
> I am using an MX916 / SXV-H9C. It is not a flat field problem;
> the distortion
> is that stars are mostly comatose. The chip does not seem
> unreasonably large
> for this reducer. I shall carefully check the distance factor,
> but I was using
> Meade's supplied spacer.
>
> Thanks.
>
> Lawrence Harris
>
>



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